CDAS is a web-based submission and tracking system for the use of data from the National Lung Screening Trial (NLST) and the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. Interested investigators can register with CDAS and request access to data from either screening trial. All requests are reviewed by NCI trial leadership. Upon approval, investigators are granted access to the requested data for a limited period. CDAS provides extensive documentation for each trial including a summary of the trial, a description of the data collected, and a searchable list of research projects and publications. Long term objectives for CDAS include integration of data from other cancer screening trials such as the LSS Feasibility Study, the HIP Breast Cancer Screening Trial, the Minnesota Fecal Occult Blood Screening Trial, and the Mayo Lung Cancer Screening Trial.